1. Field of the Invention
This invention relates to a waste heat recovering device using an oil injection type screw expander and is utilizable for recovery of waste heat discharged from plants.
2. Description of the Prior Art
A heat recovering device is known which is designed to recover heat from hot waste water and the like discharged from plants, on the basis of Rankine cycle utilizing a small temperature difference. This device comprises an evaporator using hot waste water or the like as a heat source to heat and evaporate a working medium, e.g., freon, a turbine which is rotated by the freon vapor from the evaporator, a condenser for cooling and condensing the freon vapor discharged from the turbine, and a freon circulating pump for circulating the freon through the system. The output shaft of the turbine is connected to a load such as a generator.
The drawback of this device is that because of the low temperature of hot waste water or the like which is a heat source, the working medium cannot be sufficiently heated, or a large temperature difference cannot be attained, with the result that the recovery of power cannot be effected to the fullest extent.
To offset this drawback, the freon vapor from the evaporator could be introduced into an additional heat exchanger, where it is superheated, and then supplied to the turbine, whereby an increase in the power recovery rate could be expected. In this case, however, since the freon, in its vapor state, enters the additional heat exchanger, the latter, which is used to superheat the freon vapor, must of necessity be large-sized. Therefore, a large space between the evaporator and the turbine is required for said heat exchanger, adding to the overall size of the device, a new drawback.